1. Field of the Invention
The present invention relates to an apparatus for inspecting whether foreign substances are adhered to a surface, and more particularly, to an apparatus used in the process of manufacturing semiconductor devices, liquid crystal display devices or the like.
2. Related Background Art
In the process of manufacturing liquid crystal display devices, for example, a pattern formed on a photomask (hereafter referred to as a "mask") is projected and exposed on a plate used as a photosensitive substrate. When a foreign substance, such as small debris, adheres to the mask during projection exposure, the image of the foreign substance is transferred to the plate along with the pattern image, thereby creating defects in the pattern. Accordingly, inspection for the presence and position of foreign substances on the mask using a foreign substance inspecting apparatus is necessary prior to projection exposure.
In particular, since the size of liquid crystal substrates has significantly increased, it is necessary to inspect for foreign substance over an area of a large substrate. With the foreign substance inspecting apparatus disclosed in Japanese Laid-Open Patent Publication 8-29353, a beam spot scans one direction on the inspected surface using one scanning lens having a wide scanning region. Furthermore, detection of foreign substances is accomplished using the scattered light from the foreign substances with respect to the beam spot while moving the inspected surface in a direction orthogonal to the scanning direction of the beam spot.
As described above, when the scanning region of the scanning lens becomes about 500 mm, for example, accompanying the increase in size of the substrate, the required diameter of the scanning lens becomes about 150 mm. As a result, production costs for the scanning lens increase greatly, and the apparatus as a whole becomes bulkier. In addition, when the substrate is not flat, focussing of the scanning lens over the entirety of a wide scanning region is difficult, so that the sensitivity in detecting foreign substances varies depending on the detection position.
In another process of manufacturing circuit patterns for liquid crystal display devices or semiconductor devices, a pattern formed on a mask is projected and exposed on a photosensitive substrate. When a foreign substance, such as small debris, adheres particularly to the pattern surface of the mask during projection exposure, the image of this foreign substance is transferred to the photosensitive substrate, thereby creating defects in the pattern. Consequently, a pellicle membrane is often provided on the pattern surface side of the mask to prevent foreign substances from adhering to the pattern surface of the mask. In this case, the effects of transferring foreign substances adhered to the pellicle membrane are a great deal smaller than the effects of transferring foreign substances adhered to the pattern surface of the mask. However, when the foreign substance adhered to the pellicle membrane has a certain size, the image of this foreign substance is transferred to the photosensitive substrate. In addition, when a foreign substance of a certain size is adhered to the back surface (the glass surface on the side opposite the pattern surface) of the mask, the image of this foreign substance is also transferred to the photosensitive substrate.
Hence, a foreign substance inspecting apparatus for inspecting foreign substances adhered to the mask and the pellicle membrane has been proposed. In the conventional foreign substance inspecting apparatus, the inspected surface is scanned by one beam spot formed by one scanning optical system using a beam with strong directivity, such as a laser beam. Furthermore, the scattered light, with respect to the beam spot, from the foreign substance on the inspected surface is detected by a light-receiving optical system.
However, when the size of the mask becomes large, the required scanning range also becomes wide. Consequently, there are many cases where the focal length of the scanning lens in the scanning optical system is lengthened. In this case, because the separation between the scanning lens and the inspected surface is also lengthened, the diameter of the scanning lens and the size of other optical components, such as bending mirrors between the scanning lens and the inspected surface, also become larger. As a result, production costs of components such as the scanning lens increase, and the apparatus becomes bulkier.
In addition, with regard to the light-receiving optical system, because it is necessary to have a wide scanning range with the same numerical aperture (NA), the diameter of the light-receiving lens and the size of other optical components increase. As a result, production costs for components such as the light-receiving lens increase, and the apparatus as a whole becomes bulkier.
Furthermore, with the conventional technology, a glass material is used as the light-absorbing member for absorbing the mirror reflected light of the beam spot. Accordingly, as the size of the mask increases and the scanning range widens, it is necessary to maintain the length for covering the scanning range as a whole by adhering a plurality of glass members together. However, when light is incident on the adhesion region between adjacent glass members, the light is not absorbed but scattered, thereby enabling scattered light to enter the light-receiving optical system as stray light.